There are many sources of natural gas production around the world. A good fraction of these are not located near markets for natural gas. A lesser but still significant fraction of these are separated from markets by oceans or seas.
The gas from these “stranded” sources of natural gas can be acquired for heavy discounts over world prices and therefore have the potential to be economically transported to distant markets for sale.
If the sea-going transport distances are large (over approximately 500 miles), liquid natural gas (“LNG”) ships are typically used. While it takes substantial energy to liquify natural gas, the lower bulk density of LNG makes it economical for shipment over large distances. Even so, special facilities for handling and storing LNG must be available at both the port of origin and at the port of sale.
If the sea-going distances are short (less than approximately 500 miles), then it is usually more economical to ship natural gas as compressed natural gas (“CNG”). Both large ships and large barges have been proposed for transporting CNG, typically by filling large tubular pressure vessels with natural gas compressed to pressures in the approximate range of 500 psi to 5,000 psi.
A number of techniques have been proposed to optimize the economics of CNG ships and/or barges. These include, for example:                the use of low temperature to chill the gas to increase its density as described in U.S. Pat. No. 6,725,671        the use of low temperature to chill the gas plus the addition of some natural gas liquids (“NGLs”), carbon dioxide or a combination, all of which increase its density as described in U.S. Pat. No. 7,137,260        the use of activated charcoal to absorb more natural gas at a lower pressures thereby allowing the use of lower pressure storage techniques        the use of composite materials such as carbon filament wound pressure vessels thereby allowing the use of higher pressure and higher density gas storage.        
Such technologies extend the range that CNG transport becomes more economical than LNG transport. CNG transport is more economical as it has the major advantage of not requiring special, and very expensive, facilities for handling and storing at both the port of origin and at the port of sale, such as required by LNG transport. In addition, a CNG transport ship or barge is much less expensive than an LNG transport ship or barge because of the expensive containment and safety requirements of an LNG transport vessel.
In addition, there are far fewer safety requirements for CNG loading, transport and unloading as compared to LNG transport. In fact, many countries which are prime natural gas markets only allow a few LNG ports to be installed because of the potential for LNG accidents and explosions. CNG transport has fewer safety requirements, largely because natural gas is lighter than air. If the cargo escapes in gaseous form, the gas disperses and rises quickly and mixes with the atmosphere. On the other hand, liquified natural gas can remain in concentrated pools on the surface until it all evaporates and is therefore vulnerable to an ignition source and resulting concentrated explosion.
Therefore, there is a need for methods and apparatuses that can extend the range of economical CNG transport so that stranded gas producing operations can provide much needed natural gas to more and more distant markets that cannot afford or will not allow LNG facilities.